Crude oil production in 2012-13 at 20.485 million tonne was 5.8% lower than 21.76 million tonne achieved in the previous year. It was also short of 21.64 million tonne target set for the year, according to a performance report the company submitted to Oil Secretary Vivek Rae last month.
Mumbai High fields produced 9.55 million tonne of oil, lower than 9.976 million tonne in 2011-12. Output from Neelam- Heera fields in the Mumbai offshore at 2.92 million tonne as well as 2.28 million tonne of production at Mehsana oilfields in Gujarat were lower than the previous year's output.
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"The shortfall is mainly due to non-commencement of production from G-1 field in eastern offshore and overhauling of process gas compressors at Neelam filed," it said. "Decline in production from major fields, poor influx, increase in water cut and power shutdowns also affected production."
Natural gas production was however higher at 23.54 billion cubic meters as compared to 23.31 bcm in 2011-12. Its biggest field Bassein in western offshore produced 12.43 bcm of gas as opposed to 12.372 bcm in the previous fiscal.
Mumbai High field output was almost unchanged at 4.54 bcm.
Gas sales in 2012-13 were 18.6 bcm as against 18.22 bcm a year ago.
During 2012-13, ONGC made 22 oil and gas discoveries - 12 new prospects and the remaining new pool discoveries, the report said. Of these 22, nine discoveries were made in New Exploration Licensing Policy (NELP) blocks and 13 in areas the company had got on nomination basis.
"D-1, the new pool discovery in western offshore is significant as it has established a large reserves in D-1 fields; making the field third largest in western are from Mumbai High and Neelam fields," it said.
ONGC drilled 432 wells during the fiscal (109 exploration and 323 development wells), up from 417 wells spud in the previous financial year.
Also, it acquired 3,709 line km of 2D seismic data and another 11,402 sq km of 3D seismic data.